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Vinnydb

Fi BTL N2 18" 4th order box design

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Hello everybody. I am new here and need some advice. Recently I picked up a BTL N2 18 fully loaded. I slapped together a ported box to get me by but my goal is to build a 4th order and to seal it off from the trunk. I am putting this in a 2010 Audi a4 and I think I have about eight cubic feet to work with. I will be powering the sub with a Hifonics Colossus pro 5000 watt amp. 1900 RMS into four ohms. I have a sx Power Cell and 2 runs of 0 gauge wire ran through out the car right now. I am running the stock alternator which if I remember correctly is 180 amps. I will be using either the stock Audi concert system and purchasing a signal processor and adding a 4 channel amp for the door speakers, or eventually getting a good head unit (pretty much everything in the car is integrated through the stock stereo and display screen). right now I am pushing about 130 dB but I plan on getting close to 150 in a daily driver setup. I like really high SPL systems, but this is my daily driver so I'd still like some SQ. I want it to get nasty on music and not be a complete one hit wonder. I have built many many systems in the past, but only a few fourth-order designs. Right now I don't have much trunk as it is, and I'm okay with that. I am looking for a little advice as to the direction I should go with the box design. I've read a lot about ratios for 4th orders and I figure I'll go with 1:2 for simplicity sake.(possibly 2.5/5 cf. Plus driver and port displacement for 8cf.(just an idea) I know the box is going to be huge and require a lot of material. If possible I would like to either use birch or fiberglass to save on some weight. The BTL creates a lot of pressure and I don't know if fiberglass will stand up to the BTL. Also I have a 8" flared port currently in my box and would love to use it if possible instead of going with a slot port. Any sudjestions would be much appreciated. Thank you!


150 or bust

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why do you want to do a 4th order? because you think itll be loader? or because you think its good for the sub? because either way your going in the wrong direction i would say. i would suggest going with a proper, sealed off, ported enclosure firing into the cabin. the n2 isnt much for 4th orders, and trying to put one in that trunk would be a serious pain in the ass and a huge build just to end up not being as optimal as a really well designed and implemented ported box.


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The reason why I wanna do a 4th order design, is because I met a guy who has a few Fi subs in a fourth order blow through design in is s 10 pickup. I was super impressed on how it sounded. Absolutely take your breath away and it meters over 150db on a TL. I see a lot of people doing simple ported enclosures (I myself Am guilty of that) and I'm just not impressed with the output or the sound. I like the tight punchy bass of a sealed enclosure but I like the output that a ported enclosure provides. If I were to build a ported enclosures sealed off from the cabin, how many cubic feet do you think would be best? Right now I have my sub in a 4.5 cubic foot enclosure down firing and I am not impressed(the specs that Fi provides are 4.5 to 8 cubic feet) from floor to ceiling I have 17 inches to work with. I have tried every orientation from sub facing up, sub facing down, port pointed into the car, and port pointed towards the rear. IMO the best sounding so far has been down firing with port facing the rear.


150 or bust

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you need to put it in a 6 cube box or bigger

the btls wont perform like they should in a bandpass.. people say they work and im sure they do but how much are they losing in output if it was a regular ported box or a 6th order bandpass.. your friend might have subs suitable for sealed like the sp4 q or ssd.. put that sub in a bigger box and a good amp and you will be amazed

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honestly.. if you dont have the room for a regular ported box you dont have room for a bandpass.. the btl will need larger than normal on the sealed side to bring the f's down (i been told)

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Yeah his subs were the ssd models I believe. I have room for up to 8cf, but it gets tricky because I have to angle the sub back to fit. I'd almost rather recone it to a 15, but at that point, I'd just sell it and buy a pair of 12's.


150 or bust

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If i brace it properly and add enough layers, would fiberglass hold up? How about birch or fir? The box I have weighs a ton and I'd like to save weight if possible.


150 or bust

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if you have room to make the box at 8 cubes do it.. you also want to give it more port a 8 inch aero is what i would use for 1 15.

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